This invention relates to a method of die casting high melting point metals such as ferrous metals by introducing a shot of molten metal under pressure into a die cavity defined between separable repeatedly useable dies. The shot of molten metal is fed into the die cavity under pressure along a shot duct by a piston movable therein, the shot duct communicating at one end with the die cavity and being arranged to receive, at a receiving station spaced longitudinally of the shot duct from said one end the shot of molten metal which is transferred by the piston along the shot duct into the die cavity.
In order to provide a source of molten metal for each shot a suitable induction furnace is provided above the receiving station of the shot duct and in which a slug of solid metal is positioned so as to seal a pouring aperture in the base of the furnace. When electric current is passed through the coil of the furnace the slug is caused to melt progressively from the top downwardly, the part of the slug sealing the pouring aperture in the base of the furnace being the last to melt, and hence the slug forms its own seal until the whole of the slug is melted.
It is necessary to heat the slug rapidly in order to achieve a high rate of production. However, the quantity of heat required causes a high degree of superheat of the molten metal and a relatively large amount of turbulence in the melt. In order to achieve consistent operating conditions it is necessary to control both the degree of superheat and the turbulence. This requirement is however, in direct opposition to the rate of heat input required to achieve rapid slug melting and hence the desired rate of production.
The degree of superheat is affected by the position of the slug relative to the coil of the furnace and by the electric power input into the coil. It has, hitherto, been difficult to achieve low degrees of superheat without long melting times which reduce output.